This invention relates to a chuck assembly, and more particularly to a chuck with four jaws actuated by a rotary vane actuator.
The chuck of the prior art generally comprises three or four radially movable clamping jaws. Common problems of this kind of chuck are described in U.S. Pat. No. 4,718,682 issued to Zilic, et al. and U.S. Pat. No. 6,089,577 issued to Takada, et al, for example. Zilic patent relates to a chuck that is driven by a complex mechanical arrangement. Takeda patent discloses a two-drive-system fluid pressure chuck including two sets of jaw members capable of chucking a workpiece from two orthogonal directions. The chuck includes two cylinder apparatuses, a first rod, a second rod, and a cam member. The first rod is slidably disposed within the inside of the second rod.
When two sets of jaw members are actuated independently, the clamping by one set of jaw members may be influenced by the other set of jaw members that have already fixed the workpiece. Centering of the one set of jaw members cannot be achieved if the workpiece is fixed by the other set of jaw members.
In addition, in accordance with the chuck with a fluid actuator having an axial movement of piston rod, displacement of clamping jaws is limited by the stroke of the piston rod. A longer stroke of the piston rod results in a larger size of the chuck body.
The present invention seeks to preclude many of these problems.
An object of the present invention is to provide a chuck that is capable of holding a workpiece accurately.
Another object of the present invention is to provide a compact chuck with a simple construction.
There is provided a chuck having four radial jaw grooves, two pairs of opposed jaws movably provided in the grooves, a first rotary vane actuator for actuating one pair of the opposed jaws, and a second rotary actuator for actuating the other pair of the opposed jaws, an inlet for admitting fluid, and an outlet for discharging fluid. The first and second vane actuators are operated by the fluid admitted from the one inlet such that the two pairs of opposed jaws are differentially actuated by said first and second rotary vane actuators.
According to one feature of the invention, the first rotary vane actuator includes a first pressure chamber and the second rotary vane actuator includes a second pressure chamber, in which the first and second pressure chambers are in fluid communication via at least one fluid-conducting path.
According to the other feature of the invention, the first rotary vane actuator and the second rotary vane actuator share a common pressure chamber.